1. Field of the Invention
The present invention relates to a magnetic head assembly having an open yoke write head with a highly defined narrow track width and, more particularly, to a magnetic head assembly which includes the highly defined write head configured above a read head.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
A prior art write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field in the pole pieces which causes flux across the gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on moving media, such as in circular tracks on the aforementioned rotating disk.
In the prior art write head the second pole piece layer is directly above the first pole piece layer with only the aforementioned insulation stack located therebetween. Unfortunately, when the coil layer induces magnetic flux in the first and second pole pieces there is a portion of this flux that leaks between the first and second pole pieces which causes a reduction in a write signal across the gap. This loss is sometimes compensated for by increasing the number of turns of the pancake-shaped coil layer. An increase in the number of turns in the coil layer, however, increases heat within the head. The heat can cause a protrusion of an overcoat layer at the ABS due to expansion of the insulation stack. Further, the overlying relationship of the first and second pole pieces results in magnetic leakage which degrades the data rate performance. This means that there are less bits of information written by the write head per inch of track on the rotating disk. Accordingly, there is a strong felt need to provide a write head which has less leakage between the first and second pole pieces and improved heat dissipation.
The aforementioned problems were overcome in a commonly assigned U.S. Pat. No. 5,164,869. In this patent, first and second pole pieces formed an open yoke configuration and a coil wound around the first pole piece, and then wound around the second pole piece. With this arrangement there was less flux leakage between the first and second pole pieces and there was better heat dissipation because of short coil length. In the patent, a flux guide structure for a read head was located between the first and second pole pieces. The first and second read gap thickness along with the flux guide thickness becomes the total thickness of the write gap. Unfortunately, the write gap of the write head was restricted by the read head requirement. Further, since front portions of the first and second pole pieces at the ABS served as first and second shield layers for the flux guide, the track width of the write head could not be reduced below the width of the flux guide of the read head at the ABS. This restraint prevented optimizing the write head. Accordingly, there is strong-felt need to decouple the requirements of the write head portion from the requirements of the read head portion in order to permit the write head to have a narrow track width.
The present invention is an improvement of the aforementioned commonly assigned U.S. Pat. No. 5,164,869 which is incorporated by reference herein. In the present invention the improved write head is located on top of the read head. Accordingly, the present write head has an independently optimized write gap compared to the write gap taught by the aforementioned patent. The present write head includes first and second pole piece portions wherein the second pole piece portion has front and back layer portions. The front layer portion extends from the ABS, the back layer portion extends from a back gap site and the front and back layer portions overlap and magnetically engage one another at a site that is located between the ABS and the back gap. Accordingly, the write coil can be constructed on the first pole piece portion and the back layer portion of the second pole piece portion, leaving the front layer portion for a separate construction step. This allows the front layer portion, which defines the second pole tip, to be constructed with a very narrow track width at the ABS. This narrow track width allows more tracks to be written on a rotating magnetic disk which increases the magnetic storage capability of a disk drive that employs the write head. Further, the separate front layer portion of the second pole piece permits this component to be constructed of a high magnetic moment material that is higher than the magnetic moment of the material of the first pole piece portion and the material of the back layer portion of the second pole piece portion. This, in turn, permits the thickness of the front layer portion to be reduced which, in turn, permits construction of a still more narrow track width. The present invention also enables the first pole piece portion and the back layer portion of the second pole piece portion to be planarized.
An object of the present invention is to provide an open yoke write head which can be constructed with a narrow track width without impacting performance of an accompanying read head.
Another object is to provide an open yoke write head wherein a second pole tip portion has a narrow track width and a high magnetic moment.
Other objects and advantages of he invention will become more apparent to those skilled in the art after considering the following detailed description in connection with the accompanying drawings.